1. Field of the Invention
The present invention relates to methods and apparatuses seeking to evaluate hydration of the skin and/or the mucous membranes. The invention is particularly advantageous for evaluation of the lips.
2. Discussion of Background
The term “hydration” designates the water content in the skin and on its surface, including water that comes from transpiration.
U.S. Pat. No. 6,370,426 describes an apparatus for measuring hydration of the human skin. The apparatus includes means for measuring variation in impedance between two electrodes in electrical contact with the skin. Patent application WO 02/056766 also describes an apparatus that is quite similar.
The German supplier Courage & Khazaka sells a corneometer under the reference CM825® for measuring the capacitance of the stratum corneum. The measurement is based on the difference in dielectric constants that exists between water and other substances present in the skin, thereby establishing a relationship between capacitance and the proportion of water in the surface layers of the skin.
Proposals are made in patent application EP 1,177,766 and U.S. counterpart application 2002/0107456 to use a sensor including an array of non-optical detection cells, in particular capacitive cells, for obtaining information concerning the microrelief of a non-dermatoglyphic region of the human body, for example the surface density of skin lines, the anisotropy coefficient of the density of said lines, and the number and size of pores in the skin.
Applications WO 01/24700 and DE 199 36 097 describe devices and methods of authentication by fingerprint analysis.
Application WO 01/24700 describes analyzing possible variation, due to perspiration, of the image acquired by means of a sensor so as to confirm to the authentication system that the finger whose imprint is being analyzed is indeed alive.
DE 199 36097 describes adjusting a sensitivity threshold in fingerprint recognition as a function of skin moisture.
The above documents relate to methods and apparatus which do not seek to deliver information relating to skin hydration in a form that can be understood directly by an individual, in order to inform the individual about the state of the skin.